Line Follower Robot

Line follower is an autonomous robot which follows either black line in white are or white line in black area. Robot must be able to detect particular line and keep following it.

For special situations such as cross overs where robot can have more than one path which can be followed, predefined path must be followed by the robot.

In the following section, we will discuss the line follower robot which follows black line in white area and take right turn whenever cross overs or Y shaped turn arrives.

However with some minor suitable changes, users can make robot for other possibilities also.

Video

· BLOCK DIAGRAM

Let us see how the line follower robot works. First see the block diagrams.

· EXPLANATION OF BLOCK DIAGRAM

An array of sensor is used to detect the line. Based on the status of sensors, special circuit or controller decides the position of line and also the required direction of motion required to follow the line. Motor driver circuit is used to ON/OFF the LEFT/RIGHT motors of the robot to provide desired motion.

· SENSORS

Sensors are required to detect position of the line to be followed with respect to the robot’s position. Most widely used sensors for the line follower robot are PHOTOSENSERS. They are based on the basic observation that “the white surface reflects the light and the black surface absorbs it”.

Sensor circuit contains emitter, detector and comparator assembly.

· PHOTOSENSORS

IR or VISIBLE light is emitted from the emitter (IR light is mostly preferred to avoid interference from the visible light which is generally around the robot. However IR light is also present in atmosphere but its intensity is much less than that of visible light, so IR light can give much reliable output. For better accuracy of the sensors, they must be covered properly for the isolation from the surrounding.)

This emitted light strikes the surface and gets reflected back. If the surface is white, more intensity of light gets reflected and for black surface very less intensity of light is reflected.

Photo detector is used to detect the intensity of light reflected. The corresponding analog voltage is induced based on the intensity of reflected light. This voltage is compared with the fixed reference voltage in comparator circuit and hence it is converted into logic 0 or logic 1 which can be used by the controller.

The comparator circuit may be designed in two ways.

Case-1

Black area=1

White area=0

Case-2

Black area=0

White area=1

In the following section, case-1 is used.

Sample circuit for the sensor is as shown in fig.

· EMITTER CIRCUIT

· OP-AMP PIN OUT

· PIN DESCRIPTION

Vcc is 5V power supply.

Input+ is non-inverting input terminal of an op-amp =V(+).

Input- is inverting input terminal of an op-amp=V(-).

Output is either logic1 or logic 0 depending upon both input terminals.

Output is Logic 1 if V(+) > V(-)

Logic 0 if V(+) < V(-)

· DETECTOR CIRCUIT

A= centre point of voltage divider circuit (always 2.5V)

B= Non-inverting terminal of OP-AMP

C= Inverting terminal of OP-AMP

D=Output terminal of OP-AMP

· WORKING OF DETECTOR CIRCUIT

· When light falls on detector D2, a voltage drop of around 0.7V occurs across D2 and hence 2.5V (voltage at A) – 0.9^*V (drop across D2) = 1.6^*V (voltage at C)

· When light does not falls on detector D2, no current flows through it and hence voltage at C = Voltage at A =2.5V

^*These values will be change with change in atmosphere, lighting conditions etc. We have to change variable resistor to get the desired output.

Now let us see various conditions as given in the table below.

Voltage at A	Voltage at B	Voltage at C	Voltage at D	output
2.5V	Less than 2^*V	If light falls,(white area) 1.6^*V	0V	Logic 0
2.5V	Less than 2^*V	If light does not fall,(black area) 2.5V	Vcc=5V	Logic 1
2.5V	Greater than 2^*V	If light falls,(white area) 1.6^*V	Vcc=5V	Logic 1
2.5V	Greater than 2^*V and less than 2.5V	If light does not fall,(black area) 2.5V	0V	Logic 0

If voltage at C is greater than 2.5V, the output will be always at logic 1. This condition must be avoided.

^*These values will be change with change in atmosphere, lighting conditions etc. We have to adjust variable resistor to get the desired output.

· LDR (LIGHT DEPENDENT RESISTOR)

It is a special type of resistor. Its resistance is dependent upon the intensity of light falling upon it.

It has wide range of resistance depending upon the intensity of light. Its resistance can vary from few ohms to some kilo-ohms or even more.

To use LDR, above circuits with the following modifications can be used.

1. Use visible LED instead of IR emitter.

2. Replace detector with LDR.

Controller & Motor Driver

· CONTROLLER

It is the most important part of the line follower robot. It reads the sensor’s output and based on it, drives the motor’s motion.

Let us see how to decide motor’s motion based on 8 possible combinations of three sensors.

Sensors give logic 1 for black area and logic 0 for white area. Robot has to follow black line on white surface.

Here is the truth table for it.

LEFT SENSOR	MIDDLE SENSOR	RIGHT SENSOR	STATUS	DECISION
0	0	0	NO LINE	FORWARD*
0	0	1	LINE AT LEFT SIDE	LEFT TURN
0	1	0	LINE AT CENTRE	FORWARD
0	1	1	LINT AT CENTRE & MIDDLE (SHARP LEFT TURN )	TURN LEFT
1	0	0	LINE AT RIGHT SIDE	TURN RIGHT
1	0	1	LINE AT BOTH SIDES(Y SHAPER TURN)	RIGHT TURN*
1	1	0	LINE AT CENTRE & RIGHT SIDES(SHARP RIGHT TURN)	RIGHT TURN*
1	1	1	LINE AT ALL SIDES (CROSS OVERS)	RIGHT TURN*

*=> In these situations, take decision as per your application.

· MOTOR DRIVER IC

L293 is one of the most widely used IC for motor driving. One IC can drive two different motors independently.

Pin-out for the L293 is as shown in fig.

· PIN DESCRIPTION

E1 & E2- logic 1 (5V) to enable M1 or M2 respectively. Both the pins can be controlled either from controller or by directly connecting 5V power supply.

Pin 8- Voltage required to drive motors-It can be 9V or 12V.

Vcc- 5V power supply

M1-B-=to drive M1 in forward direction

M1-A =to drive M1 in reverse direction

M2-A=to drive M2 in reverse direction

M2-B=to drive M2 in forward direction

These pins must be driven by controller.

We do not need reverse motion here. So M1-A and M1-B will be set at logic 0.

Hence for various motions of robot, see the following truth table.

Circuit Diagram & IMP Guidelines

· CIRCUIT DIAGRAM OF LINE FOLLOWER ROBOT

Check the Circuit Diagram Tab

· CIRCUIT CONNECTIONS

1. There are three sensors. They are connecter with microcontroller P89V51RD2BN as

a. Left sensor= Pin P0.2

b. Middle sensor=Pin P0.1

c. Right sensor=Pin P0.0

2. Motor driver IC L293 gets four inputs from P89V51RD2BN as

a. M1-A=P2.0

b. M1-B=P2.1

c. M2-A=P2.2

d. M2-B=P2.3

3. Left side motor is M1 and right side motor is M2.

· IMP GUIDLINES

(1. Usually three sensors cannot provide sufficient accuracy because if one sensor fails to detect a line, robot will be out of the track.

The most efficient solution is to increase the number of sensors. This change can change the program more complex.

The best way is to use more sensors and use the program of three sensors given below. Let us see how this is possible.

Suppose we wish to use three sensors (l1, l2, l3) on left side, two sensors (m1, m2 )at middle and three sensors (r1, r2, r3) on right side.

Now left sensor= l1+l2+l3

Right sensor=r1+r2+r3

Middle sensor=m1+m2

+ shows Boolean or operation.

Now eight sensors can be represented using three sensors only and the given code can be used. Such arrangement will improve the accuracy of the robot.

(2. Assume black line to be followed in white area.

Analyse the track to be followed. If it does not contain the missing lines than when all the sensors shows white area, it means robot has gone out of the track. At such condition provide the reverse motion to robot so robot will automatically detect the find the line again. If you will not provide reverse motion, you may have to face penalty. Using this idea you can avoid it.

HARDWARE REQUIREMENTS & PREPARATION

· HARDWARE REQUIREMENTS

In this robot, very few hardware elements are required. You need following things.

1. Body of PLY/PLASTIC/METAL etc.

It is required to enclose the entire robot within it. You can make robot in which circuitry is visible. In such case, you need a base only.

Many types of materials are available which can fulfil the requirements, but thin sheet of PLY is the best choice as drilling and fitting of assemblies on ply is very easy.

2. PVC/PLASTIC pipe

It is required for proper alignment of motors. You can fit motor at each end of the pipe so that any misalignment between motor’s axis is avoided which will improve performance of robot on track while moving.

3. Clamps, screws & screw driver

Combine assembly of motors and pipe can be fitted on base of robot using clamps and screws.

4. Drilling Machine

It is required to drill holes on base of robot for screws.

· STEP BY STEP HARDWARE PREPARATION

1. First prepare GPBs/PCBs of sensors, controller’s working environment and motor driver assembly and provide interconnections between them also.

2. Select base material (we assume it as a PLY) and shape of it.

3. Calculate approx. space required for individual circuits and prepare a plan how they will be placed.

4. Draw the plan on ply. Provide some margins.

5. Cut ply as per the plan.

6. Drill holes at corners of circuits and at their respective position on base.

7. Fit the circuit with base with the help of screws.

8. Now your robot is ready.

9. If you want, you can cover the entire robot in suitable body.

10. Isolate sensors from atmosphere so that their performance is not affected by atmospheric light, camera flashing etc. (This is very much essential when you are using IR sensors/ LDR etc.)

Project Source Code

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#include<reg51.h>
//forward=0x09;value to be put on P2 for forward motion
//left turn=0x08; value to be put on P2 for left turn
//right turn=0x01; value to be put on P2 for right turn
//P0 as input port-connected to sensors
//P2 as output port-connected to L293-motor driver IC
 
void delay(unsigned char di)                          //delay subroutine
{
      unsigned char dii;
      unsigned int d;
      for(dii=0;dii<di;dii++)
            for(d=0;d<1275;d++);
}
void main()
{
unsigned char msg[8]={0x09,0x08,0x09,0x08,0x01,0x01,0x01,0x01};
unsigned char a;
while(1)                       //repeat forever
{
a=P0 & 0x07; //read sensors and mask upper 5 bits(bit 3 to 7) of P0
P2=msg[a];      //select the desired value from array msg based on sensors //position
delay(10);        //provide delay
}
} 
 
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